Though Reid only names three examples of instances when more than one independent serial killer has been active in the same area at the same time, there are several more examples, including (but not limited to):

Derrick Todd Lee, a.k.a. "The Baton Rouge Serial Killer", was active in Baton Rouge, Louisiana, at the same time as Sean Vincent Gillis, who actually feared being "outdone" by Lee.

Lonnie David Franklin, a.k.a. "The Grim Sleeper", was initially believed to be an unrelated serial killer referred to as "The Southside Slayer", who turned out to be at least four independent killers, Louise Craine (who committed at least two of the Slayer's murders), Michael Hughes, Daniel Lee Siebert, and Ivan Hill (the latter three of whom were attributed to at least one Slayer murder each).

In addition, an unrelated series of murders, which was erroneously dubbed the "Strawberry murders", began in succession of the murder of Debra Jackson, a victim of the Sleeper; these murders had a similar M.O. to Jackson's murder.

Serial killers Joel Rifkin and Robert Shulman were both active in the Suffolk and Nassau counties of Long Island, New York, at the same time; they even lived a few miles away from each other and killed some of their victims on the same days.

After Rifkin's arrest in 1993, Shulman then shared the same area of operation with an unidentified third serial killer known as (among other names) the Gilgo Beach Killer until his own arrest in 1996.

Serial killers Anthony Sowell and Joseph Harwell were both active in Cleveland, Ohio, at the same time.